The long-term goals of the research program are to (1) explicate the cognitive processes underlying Attention-Deficit/Hyperactivity Disorder (ADHD) and other disorders of attention and action, and (2) delineate the role of these processes in the development and maintenance of the disorders. Research on cognition in ADHD points to two domains of impairment-control of attention and action corresponding to the behavioral dimensions of inattention and hyperactivity/impulsivity. A working hypothesis that can integrate these findings is that individuals with ADHD have disturbances in the control of attention for guiding action. The specific aim of the proposed study is to test the integrity of discrete processes involved in control of attention and action in children with ADHD. The processes are: (1) allocation of attention in accordance with task demands, (2) maintenance and manipulation of spatial and temporal information in working memory, (3) ability to execute sequences of rule-governed actions, and (4) ability to inhibit motor programs in accordance with task demands. These processes will be tested using manual and saccadic response times, task-evoked pupillary responses, and accuracy measures. The hypothesis is that compared to controls, children with ADHD will show intact performance on tasks assessing lower-level processes (e.g., ability to execute random sequences of actions), but impaired performance on tasks assessing higher-level control of attention and action (e.g., ability to execute rule-governed sequences of action s). Taken together, results of this stud y can delineate the nature of impairment s in attention and action in ADHD. This knowledge, in turn, will advance understanding of the neurobiological bases of the impairments, and lead to improvements in diagnosis, assessment, treatment, and prevention of ADHD and other disorders of attention and action.